1. Field of the Invention
The present invention generally relates to the field of removing a layer of material from a semiconducting wafer, and more specifically to the detection of an end-point for chemical mechanical polishing (CMP) of a semiconducting wafer by way of an optical surface analyzer (OSA).
2. Description of Background Art
Chemical Mechanical Polishing (CMP) is used in the semiconducting manufacturing process to flatten and/or remove a layer of material from the surface of wafers. The CMP process is used to planarize the surface of a coated and patterned silicon wafer. To control the CMP process engineers want to measure the amount of material removed from the metal region as compared to the oxide region. Since the oxide and the metal areas have different mechanical properties they will polish at different rates. It is desirable to detect when the polishing equipment has removed a layer of material (copper, for example) from the surface of the silicon wafer. This process is known as end-point detection.
The conventional technique for detecting the end-point for polishing materials involves processing die-to-die images to identify where the material (i.e. copper) residue is located. Typically a camera based imaging system will acquire an image of a die and compare it to a stored image taken on a perfectly clean die. Other techniques involve ellipsometry as well as profilometry to determine the effect of CMP on the surface. The drawbacks in performing a die-to-die match to determine end-point processing are apparent in the relatively slow processing time of this manual process. Also, the process of matching die-to-die images produces results that are qualitative in nature and limited to information regarding the uniformity of a polishing cycle. These methods are silent with regards to quantitative measurements pertaining to the amount a material has been over-polished or under-polished.
What is needed is a system and method for automated detection of the end-point in the process of removing a material by polishing and a quantitative analysis of the amount of material that is over-polished or under-polished.